(a) Field of the Invention
The present invention relates to a heat recovery unit for use in an industrial process to preheat fresh air such as cold air taken from the outside, with hot air produced in the process, such as the hot air exhaust from a dryer.
More generally, the present invention relates to an air/air heat recovery unit making use of water as heat transfer medium.
(b) Brief Description of the Prior Art
Air/air heat exchangers are well known in the art and commonly used in numerous industrial processes to preheat fresh air taken from the outside with hot air generated during the process, prior to disposing of the same.
These known heat exchangers usually comprise two adjacent compartments having at least one heat-conducting wall in common, each compartment being provided with an air inlet and an air outlet. The hot air whose heat is to be recovered, is passed through one of the compartments of the heat exchanger. The fresh air to be warmed is passed through the other compartment, either in the same direction as the hot air, in opposite direction thereto (countercurrent) or even in angled direction. Heat exchange between the hot and fresh air flows occurs by heat conduction through the conducting wall common to both compartments.
These known air/air heat exchanger are rather efficient as far as heat exchange is concerned. However, they have the major drawback of being very difficult to control as the only way of adjusting the amount of heat exchange is to vary the flow rate of fresh air and/or hot air through the compartments.
In other technical fields not directly related to heat exchange, industrial apparatuses are known, which comprise a tank having a lower liquid space and an upper gas space on top of the liquid space, a liquid inlet and a liquid outlet, a gas inlet and a gas outlet and at least two rotary driving shafts parallel to the longitudinal direction of the container, each shaft supporting a plurality of rotary discs mounted and sized in such a manner that the discs on one shaft overlap without contacting the discs of the other adjacent shaft(s) and, simultaneously, dip into the liquid in the tank.
Industrial apparatuses of this type are disclosed by way of examples, in Canadian Pat. Nos. 381,991 and 565,908, for scrubbing a gas with a liquid in such a manner as to remove the impurities contained in this gas. Another industrial apparatus of this type is disclosed, by way of example, in Canadian Pat. No. 746,331, for humidifying the air exhaust from domestic, hot air heating system. Another industrial apparatus of the same type is disclosed in Canadian Pat. No. 944,887, for reacting a liquid, namely a solution of a high molecular weight polymer, with a reactive gas. In this particular case, the apparatus acts as a gas-liquid contact reactor.